Advances in semiconductor processing and circuit design have led to increased component density in very large scale integrated (VLSI) circuit arrays. While the individual components comprising such circuits operate at low voltage and draw very low currents, the increased density of the components in such circuits has a consequential increase in heat generated per unit area of semiconductor chip surface. This has necessitated the use of heat conducting pedestals and heat exchangers attached to the chips to facilitate the removal of heat from the chip surface. An overview of state of the art heat removal is contained in the article "High Heat from a Small Package" appearing in the March 1986 edition of "Mechanical Engineering."
Heretofore, a variety of heat exchangers have been suggested as a means for mounting semiconductor devices and additionally serving as the means for transferring the chip heat to a flowing gas or liquid coolant. Examples of such prior art include the Jackson U.S. Pat. No. 2,942,165, the Butt U.S. Pat. No. 3,327,776, the Laermer U.S. Pat. No. 3,706,010, the Klein U.S. Pat. No. 4,151,548, the Pellant U.S. Pat. No. 4,188,996, and others.
A common difficulty with devices of the prior art is their construction which typically does not allow a reliable means for electrical leads and fasteners to pass through the thickness of the fluid passage. Additionally, devices of the prior art are susceptible to fluid leakage due to eventual failure of joints or seams which have been bonded or soldered to prevent fluid leakage to the environment Such failures are likely when the device is operated in a high vibration environment or when the pressure of the working fluid is high. Finally, devices of the prior art are limited to substantially thick cross sections due to the methods of fabrication taught by their inventors. Such thick cross sections impose undesirable weight and space penalties in electronic systems, especially those found in high speed computers and airborne electronic equipment.
With regard to the S. P. Jackson et al U.S. Pat. No. 2,942,165 entitled "Liquid Cooled Current Rectifiers," it is to be noted that Jackson's pin arrays are discrete pin clusters which can be inserted and removed from the fluid passage. The pin fins in the Jackson device are not integral with the walls of the heat exchanger, and most importantly, the Jackson heat exchanger cannot be drilled through its cross section without breaching the fluid cavity and causing a leak. The Jackson device certainly does not teach a seamless heat exchanger having a very thin cross section, as in the instant invention, nor does Jackson teach inlet and outlet tubes integral with the finned core of the heat exchanger.
The A. G. Butt U.S. Pat. No. 3,327,776 entitled "Heat Exchanger" is constructed from a number of individually fabricated parts, including fins, top, bottom, end plates and mounting columns and the like, and it quite obviously contains many joints and seams requiring effective means for sealing against fluid leaks. The Butt device is of the class of devices sought to be improved upon by the present invention, where no sealing techniques are needed in view of its freedom from seams and joints.
The Haumesser et al U.S. Pat. No. 3,328,642 is concerned with the cooling of electronics by the use of meltable material, such as sodium. Although at a selected temperature the material in the reservoir melts and absorbs large quantities of heat, after all the material has melted, the temperature of the reservoir and the liquid increases, with the temperature of the electronic components likewise increasing until such ti me as the electronics fail. It is therefore to be seen that the Haumesser et al patent relates to a device with which continuous operation is impossible.
The Chu et al U.S. Pat. No. 3,524,497 involves the use of relatively large pins protruding into a fluid cavity from one wall, and quite importantly, those pins could not be drilled through without causing a fluid leak. The Chu et al arrangement is to be contrasted with the present invention, wherein seamless pins extend the full distance of the fluid cavity and are permanently joined to the two opposing walls, with no chance of leakage.
The Laermer et al U.S. Pat. No. 3,706,010 represents a heat exchanger formed from at least two separately machined parts joined together. Presumably the end walls and tubes conveying fluid to and from the core would also be attached by brazing or adhesives. That teaching is to be contrasted with the instant novel method and novel construction involving a single fluid passage taught herein, for the present novel heat exchanger is seamless in that it is formed as a single piece or component, thus not requiring the use of adhesives or brazing.
With regard to the Peck U.S. Pat. No. 3,971,435, it involves a totally enclosed transfer device or "heat pipe" containing a fixed amount of fluid which never passes beyond the boundaries of the device. Peck uses parallel grooves to convey the liquid coolant from one end of the heat pipe to the other, which grooves are covered with a perforated plate. The space above the perforated plate conveys the same coolant in its gaseous state. It is important to note that Peck's unit cannot accommodate electrical leads from any electronic device mounted directly to it, for any hole drilled in the Peck device would create fluid leakage and subsequent failure.
The Ruka et al U.S. Pat. No. 4,057,101 is somewhat similar to the previously mentioned Haumesser et al patent, as it features a totally sealed heat sink containing a meltable material in a honeycomb structure. It is important to note that, in steady state operation, the amount of heat removable in accordance with the Ruka et al teaching is quite limited inasmuch as the heat exchanger would be in poor thermal contact with the electronic devices. Obviously, this patent cannot be construed as representing a seamless device, or a device in which liquid may flow through it continuously as in the instant invention.
With reference to the Klein et al U.S. Pat. No. 4,151,548, it teaches a heat exchanger with a single fluid passage with multiple pins extending the height of the passage, with such pins being of a structure integral with the top and bottom walls. Significantly, Klein utilizes a two-piece construction wherein identical halves are soldered together, which of course is to be contrasted with the present invention, which utilizes a single component construction free of seams and therefore not requiring any soldering type efforts.
The Pellant et al U.S. Pat. No. 4,188,996 is a liquid cooled heat exchanger comprised of two separately fabricated parts, which are subsequently soldered or glued together, with separate tubes for conveying coolant to and from the heat exchanger being attached, presumably by soldering or glueing. Although it might be possible to drill holes through Pellant's device, such drilled holes would necessarily have to pass through a glued or soldered seam, thereby creating a potential for fluid leakage. This is to be contrasted with the present invention wherein there is virtually no chance of leakage of any kind
With regard to the Frieser et al U.S. Pat. No. 4,312,012, this amounts to a technique for enhancing boiling heat transfer, and this is not really a heat exchanger device. Any electronic devices would need to be mounted inside the fluid cavity in accordance with the Frieser et al teaching, and no fluid flow can take place, which is to be contrasted with the instant invention, wherein a substantial amount of cooling takes place as a result of the flow of a coolant fluid. A further distinction of the instant invention is that it necessitates none of the external fins employed by Frieser et al.
The Parmerlee et al U.S. Pat. No. 4,315,300 teaches the utilization of a plurality of printed circuit boards in a parallel relationship between two side plates, with the side plates containing a fluid passage for conveying liquid coolant from the printed circuit boards. Many distinctions are apparent here, for Parmerlee utilizes forced air over the electronic components to obtain partial cooling, whereas the instant invention does not rely on air or any other gas for cooling.
Concerning the Tuckerman et al U.S. Pat. No. 4,450,472, it teaches the cooling of a single semiconductor integrated circuit utilizing a plurality of parallel and closely spaced rectangular channels of microscopic size etched onto one side of a silicon chip, with the integrated circuit being applied to the opposite side of the chip. Cooling liquid is forced through microchannels to cool the integrated circuit. This of course is a construction quite different than the present invention, wherein several chips may be mounted to a separate heat exchanger, rather than the single chip arrangement taught by this patentee.
Regarding the Pease et al U.S. Pat. No. 4,567,505, it is concerned with a method of attachment between a chip and a heat sink, wherein specially shaped microscopic grooves are formed in the heat sink. The mating surface must be flat and smooth, and a liquid place between the two surfaces partially fills the grooves and, by capillary action, causes a significant attractive force between the two mating surfaces. There obviously is no consequential similarity between the Pease et al patent and the instant invention, for the instant invention teaches a novel heat exchanger construction, whereas Pease is concerned with a method of attachment between a chip and a heat sink.
It was in an effort to overcome the many disadvantages of the prior art devices that the present invention was evolved.